The present invention relates to a tube expanding device that expands tubes from the inside diameter thereof.
Generally, in the process of manufacturing an heat exchanger such as a boiler, condenser, or radiator, when a tube is joined and fixed to a tube plate, tube expanding tools are used for expanding tubes from the inside diameter and pressing it against the tube plate (e.g., see Japanese Laid-open Utility Model Publication No. H07-15128, Japanese Laid-open Patent Publication No. H07-290171, and Japanese Laid-open Utility Model Publication No. H01-143632).
For example, the tube expanding tool described in the above-mentioned Publication No. H07-15128 is constructed so that an operator couples the tube expanding tool to a rotary drive machine to rotate rollers, and by pressing the rollers against the inner peripheral surface of the tube and rolling them, a tube expanding operation can be simply performed. With this tube expanding tool, the expanded portion of the tube is formed with a smooth continuous surface whose radius of curvature is small, so a finish of high-quality tube expanding that maintains a true circular shape is possible.
The construction of the tube expanding tool described in the above-mentioned Publication No. H07-15128 will be explained concretely with reference to FIGS. 7A and 7B, in which FIG. 7A is a sectional view for explaining a conventional tube expanding tool, and FIG. 7B is a part-plan view showing the positional relation between a roller and a mandrel.
As shown in FIG. 7A, the tube expanding tool 121 includes a tapered mandrel 123 formed integrally with a coupling portion 122 that is coupled to a rotary drive machine (not shown); a plurality of rollers 124 with a reverse taper shape conforming to the taper shape of this mandrel 123; and a frame 125 for freely rotatably holding the rollers 124 on the outer peripheral surface of the mandrel 123.
As the rotary drive machine to which the tube expanding tool 121 is coupled, a manually operated type rotary drive machine is generally used, which is held by operator's hands during a tube expanding operation and includes a controller for controlling the rotation and stop of the rotary drive machine by detecting a load torque during the tube expanding operation.
As shown in FIG. 7A, in the tube expanding tool 121 constructed as described above, if the mandrel 123 coupled to the rotary drive machine is moved forward relative to the frame 125 by an operator, that portion of the mandrel 123 which is large in outside diameter abuts on the rollers 124 gradually and therefore the rollers 124 are pushed out radially outward from the outer peripheral surface of the frame 125 and are pushed against the inner peripheral surface of the tube TU. In this state, if the mandrel 123 is caused to make positive rotation (rotation in an A direction, i.e., right-handed rotation as viewed forward from the rear end of the tool) by the rotary drive machine, the rollers 124 revolve around the mandrel 123 in the clockwise direction (the same direction as the direction of rotation of the mandrel 123) while making reverse rotation (rotation in an R direction, i.e., left-handed rotation as viewed forward from the rear end of the tool).
That is, by rotating the mandrel 123 by the rotary drive machine (not shown), the rollers 24 are rotated, and when the rollers 124 is being revolved around the mandrel 123 together with the frame 125, the rollers 124 are rolled on the inner peripheral surface of the tube TU, whereby an expanded diameter is formed (this rotating system is referred to as a mandrel rotating system).
As shown in FIG. 7B, each roller 124 is held at a feed angle θ to the mandrel 123 by the frame 125 (see FIG. 7A), so if the rollers 124 are reversely rotated, the mandrel 123 is moved forward. As a result, the rollers 124 are automatically pushed out outward from the outer peripheral surface of the frame 125.
However, in the tube expanding tool 121 of the conventional mandrel rotating system, the mandrel 123 is rotated by the rotary drive machine, and the rollers 124 are rotated by the rotation of the mandrel 123, so that the frame 125 is rotated by revolving the rollers 124 around the mandrel 123. For that reason, the rollers 124 perform a planetary gears motion between the inner peripheral surface of the tube TU and the mandrel 123.
Therefore, by the principles of the planetary gears motion, the rotation speed of the frame 125 is reduced to about ⅓ to ⅕ of that of the mandrel 123, depending upon the diameters of the mandrel 123 and roller 124. For that reason, there has been a problem that the rotation speed of the roller 124 (frame 125) does not increase, while the tube expanding operation is time-consuming and the working efficiency is low.
Hence, to raise the rotation speed of the roller 124, it is conceivable to raise the rotation speed of each rotary drive machine, but in this case, runout of the mandrel 123 and rollers 124 will occur and cause vibrations. For that reason, forming quality such as a degree of true circle deteriorates and a burden to an operator becomes great. Besides, if the rotation speed of the rotary drive machine is raised, after the tube expanding operation the braking reaction force in stopping the rotary drive machine will become great, thereby resulting in a reduction in the working efficiency and handling convenience.
On the other hand, if the feed angle θ is made larger to shorten the tube expanding time, an angle at which the axis of rotation of the roller 124 intersects the axis of rotation of the tube TU becomes larger and the formed shape of the tube expanded portion EX is easy to become a hand drum shape whose central portion is dented. For that reason, there is a possibility that the problem of strength and airtightness in joining and fixing the tube TU to the tube plate will occur.
In addition, if the taper angle of the taper-shaped mandrel 123 is made larger to shorten the tube expanding time, the mandrel 123 must be pushed strongly to an extent that the forward movement of the mandrel 123 is reduced. For that reason, a load applied to each member increases and results in shortening of the life time of the tube expanding tool.
Besides, the controller connected to the tube expanding tool 121 is used for controlling the operation from the state in which the mandrel 123 has abutted on the rollers 124 to the state in which the rollers 124 has been pushed out by the mandrel 123. For that reason, the process of abutting the mandrel 123 on the rollers 124 and separating the mandrel 123 from the rollers 124 must be performed before and after tube expanding by the operator. Particularly, the operation of separating the mandrel 123 from the rollers 124 requires a great force and results in a burden to the operator, because the mandrel 123 is pushed against the rollers 124.
The aforementioned tube expanding tool 121 requires dedicated couplings to connect the coupling portion 122 and the rotary drive machine together. For that reason, the number of components increases and a time-consuming connection work is required. Moreover, chatter of the connecting portion sometimes occurs, thereby resulting in a contact turn of the connecting portion.
Furthermore, since the operation of pushing the mandrel 123 against the rollers 124 and separating the mandrel 123 from the rollers 124 is manually performed, a great deal of work load is required by the operator.